But a new decades-long study finds coffee didn't have protective benefits: Drinking four or more cups of joe per day can be deadly for some.

Researchers found drinking 28 cups of coffee or more per week increased a person's odds of dying prematurely by 21 percent. The risk was more than 50 percent higher in adults under 55 years old.

"There continues to be considerable debate about the health effects of caffeine, and coffee specifically, with some reports suggesting toxicity and some even suggesting beneficial effects," study co-author Dr. Carl Lavie, a cardiology researcher at the Ochsner Medical Center in New Orleans, said in a statement.

The average American adult drinks about three cups of coffee per day, according to the authors.

For the study, researchers looked at data collected between 1979 and 1998 on nearly 44,000 people between 20 and 87 years old who answered health surveys about their personal and family medical histories, and lifestyle habits -- including how much coffee they drank. Most of the study participants were men.

Researchers followed up with them for about 17 years, and found more than 2,500 deaths occurred, 32 percent of which were caused by heart disease.

Younger men who drank about 28 cups per week were 56 percent more likely to die prematurely from any cause than those who didn't drink any coffee. Younger women who drank that much java doubled their mortality risk compared to those who didn't.

The researchers said that people who consumed higher amounts of coffee were also more likely to smoke and have lower fitness levels (as measured by treadmill tests), which may have added to their health woes.

They noted though, that the link between between coffee consumption and mortality risk in men and women older than 55 wasn't statistically significant (meaning the increased numbers could be due to chance), nor was it seen to add to cardiovascular death risk.

Since previous studies have found vascular benefits from drinking coffee, what should people take from the new research?

Dr. Leslie Cho, section head of preventive cardiology and rehabilitation, and director of the Women's Cardiovascular Center at the Cleveland Clinic, told CBSNews.com that patients often get discouraged when they hear these conflicting studies finding benefits and risks from coffee, and pointed out the same goes for health studies that look at alcohol, fish oil and vitamins.

"The honest-to-goodness, best theory is everything is probably good in moderation to some extent," said Cho, who was not involved in the study. Twenty-eight cups of coffee for week is "truly an excessive amount of caffeine," she added.